RF Low Energy Plasma Beam
 

RF Low Energy Plasma Beam
  

   


^†


 


(2000

Deposition of Diamond-like Carbon Thin Film by RF Low Energy Plasma Beam

Dongsun Kim^†

School of Chemical Engineering, Kongju National University, 182 Shinkwandong, Kongju, Chungnam 314-701, Korea (Received 5 June 2000; accepted 13 November 2000)



     flux      RF ion source   


  !" #$%& ' () *+,- ./& 0 12 34& 567*.  CH48 H2 9 

 :;    flux 
<=  >? '@ RF $A   !" #$%(DC Self Bias Voltage)& BCDEF G7HI, 56@ 34 JK  LMN ./O Ellipsometer, UV-VIS Spectrometer, Raman spectroscopy P&  QR7*.  >? '  !" #$% −50 V −300 VS 5T U VW X Y 1.89 2.35S 57), −100 V −300 VS 5T U LMN Z[O 2.35 1.35S \27HI, I_D/I_G ] 0.79 4.48S 57*. ^ _8S#`, aO RF $A 'S '  !" #$%& F )Q! . /& 0 12 34 56b ) cO  !" #$%& F 56@ 34O deC(graphite) 1234 56f

& g Y hi*.

Abstract−The diamond-like carbon thin films were deposited by RF ion source which can control ion energy and flux inci- dent on the substrate without applying substrate bias voltage at room temperature. The film depositions are performed using a mixture of methane and hydrogen and changing the DC self bias voltage via RF power applied to ion accelerating grid elec- trode in order to control the energy and flux of ions bombarding the substrate. The structure and optical properties of the films are evaluated by ellipsometer, UV-VIS spectrometer, and Raman spectroscopy. The refractive index of the deposited films increases from 1.89 to 2.35 as DC self bias voltage is increased from −50 V to −300 V. The optical bandgap decreases from 2.35 to 1.35 and the ratio of I_D/I_G obtained from Raman spectroscopy increases from 0.79 to 4.48, respectively, with increasing DC self bias voltage from −100 V to −300 V. From this results it is concluded that at low DC self bias voltage (<−50 V), soft, polymer-like films are formed while at moderately high DC self bias voltage (−100 V to −200 V), diamond-like carbon (DLC) films are formed, and at high DC self bias voltage (>−300 V), graphite-like carbon films are formed due to high ion bombardment.

Key words: RF Ion Source, Diamond-like Carbon Thin Film, PECVD, Plasma Process

†E-mail: dskim@knu.kongju.ac.kr

1.  

     (diamond-like carbon(DLC) thin film)  (high hardness),   (low friction coeffi- cient),   !"#  $(high transparency), %&'

0123(smoothness) 4 5'6 78(chemical stability) 9: ; + [1, 2] <= >? @A scratch-resistant, wear-resistant, anti- reflecting, protective coating BC DEFG[3], HI DEFG[4],

JK HI LM[5], NOP Q[6], RD ST LM[6], JU V =WX NOP 5'LMY[7, 8] 4 ECR[9, 10] 9: Z2 LM [ Y :C \ -] ^_`= >.

O bcd efg LM [Y#  hic H: j<

4 flux LM`k < : ]l 4  m8c n op+

"q +[11, 12]. ?r hic H j<: Q? aO L Ms  polymer-like carbon, diamond-like carbon, tu= graphite- like carbonvw gU`k x  >. 0*  H j<# L Ms  -yc=,   z{ <|(polymer-like carbon), 0*  H j<# LM s   z{ } ~d

 39 1 2001 2

 >k# H j< 4 flux: ˜k LMs : ]l 4  •™ ~ n >k# švw p]`k < l›. 

300^oC™: H#  ¡ graphite5 V ¢5`k :

 c A˜¦ <= >. § ¨¦ ©ªc? BC 

± ²³  [Diamond-Like Nanocomposite (DLN)] ´†cZ

­5 µ^c= >[14-16]. V+,
 ¶= ·¸w# ¹ º »Š ,-vw ¼ ½¾¿  p]c= >? @A 

     À Á+ À5s 

   [Fluorinated Diamond-Like Carbon(FDLC)](k=2.0-2.4)  ´†c n -] \ c= >[17-19].

 -]# ?Ã: LM [Y :C    

  LMq * %? B# ÄÅ+ A˜¦¯ Cmc? B C H j< 4 flux: ˜k Ÿ+ NOP Æ8 :Ç+ RF

ion source cZ ?r JUÈ¿ f¾É 6c< ‹= 

     LMcÊ.  CH4 H2D

cZ ?r hic H j< 4 flux ˜kc? BC H

ºË 6s JUÈ¿ f¾É €5 ~/# _cÊv|, LMs

: ]l 4  Ellipsometer, UV-VIS Spectrometer, Raman Spec- troscopy 9 cZ gÌcÊ.

2.  

2-1.
  

 -]# ͝+ NOP Æ8 :Ç+ RF ion sourece: ´Î

 Fig. 1 dÏd >.  Æ8 Q¡ Ð ´: fgvw dÑkT

>. cd RF ion sourcefg NOP Ҝ? fg. RF ion source DÓ6SD DÔw ƒ¯k^ 3"J: ÒÕÖ: K<s ™f

¾× DÓ6SDrvw ƒ¯k^ 1 mmJ 1.8 mm ŠØ: ÏÆ6 RF¾‘ 6s cf ¾×(ºË)vw ]`k >. Ð ¾× 1 cm ÐÙ: ÕÚÖ ÓÛÜ :cZ gu`k >. ÆÅ¾Õ ÝÞ LÖ rf ßàáD matching network tu= 13.56 MHz rf ÆÅ ¾Õvw ]

`k >. Ҝ? 12' â 12' J: ÕÚÖvw DÓ6SD DÔw ƒ¯k ãv|, RF ion source =ä åG ÚcZ t B æ çx  >è é`k >. V+ Ҝ? åê ë¢ ìÛâ ?

 ìÛ: m³ :cZ ^Ævw ƒ¯k<| =^Æ É‘í8?

(Penning Gauge, Vacuum Science, INC., Korea), ,e ɑí8?(Baratron Gauge, MKS 627A, USA)w ]`k >. ?r îï ¼H ð)?

 :cZ ñò ð)cZ 20^oC ½<cÊ= Gridâ ?r îï 5 cm ókT >.

ÆÅ D¯ 3´: x{ ôõ ˜k?(mass flow controller, MKS, USA) ÚcZ 8ëö ˜k`k<= Ҝ?: ɑ ,eɑí8?

 -ms ɑ˜k?(MKS, U.S.A) :cZ throttle valve ˜kz vw÷ ˜k`è `k >. V+ ºË RF ¾‘ ÆÅzvw÷

%ø JUÈ¿ f¾É RF šF ÚcZ DC ¾É í8cÊ. 

 LMc? ¾ ?r: ùú BC 100 mTorr, −200 V Self-Bias

¾É# ûü NOPw 10g ý7 þucÊ.  LM ͝s ÿ¾ l›¯ Table 1 dÏd >.

LMs : ÐÙ thickness profilometerw eÎ í8+ ˆ Ellip- someter cZ 8ëc¡ í8z ý 
, ™(refractive Index) í8cÊ. Raman D¯ ˆ¢(backscattering) ]l Ö# k<|, í8c=È c : ¥ gC àc? BC

# ûü ST(514.18 nm) cZ 40-60 mW:  ¾‘# í 8cÊ. ' : í8 Ì! Õr LM+  UV-Vis Spectrometer(Shimadzu Model UV-160) cZ  í8cZ

¢`k^.

2-2. RF Low Plasma Beam 

RF ion sourceÕu e ¾×  RIE  ÝÞ: Õuâ ½ Fig. 1. Schematic description of the RF ion sources and plasma reactor

used in this study.

Table 1. Conditions used for the deposition of diamond-like carbon thin films

Sources gases Methane : 20 sccm

Hydrogen : 30 sccm Substrate used Silicon Wafer, KBr Disk, Quartz Disk

Power sources 13.56 MHz RF

Grid DC self bias voltage −50 Volt ~−300 Volt Reactor base pressure < 2.0j10⁻⁵ Reactor pressure 100 mTorr Substrate temperature 20^oC

Íc. cf ¾× Z? ~? Õc D¯ X êk  >

: ¾ c/ w* [¾,  NOP †%+.  N OP º: H ¾È: x{ º >k#   @A

NOP 8¾câ f¾c È: ¨B/ ­ Ö ½<c

? BC# WB ecZ 8¾B ½<+.  “NOP ¾B (plasma potential)”Oc|,  ¾B @A ¾× Ҝ? WB ¾ È mZs !" %?|  dark space(“Sheath”)O +.  Z

? WX(>1 MHz)# H¯ t¯:  x{ @A C^

UÝ eœc< c? @A ¾È¯ Ws ¾U ÿÒ¿ "q +. § l›c# NOP ¾¿ tu= sheath ¾?â 

 "q c þ ©6. @ lt+ ! ¾×# 8¾c â f¾c È N"D Ö ½<cè f JUÈ¿ ¾É(DC Self Bias Voltage) Ö`k^. Fig. 2 eÖ ¾×  NOP

Ҝ?# Ö`k< NOP ¾B, sheath¾B, tu= DC Self Bias Voltage ecZ # $Í`k >[20]. § JUÈ¿ f¾É

ÕÚÖ K<s ™f ¾× RF ¾‘ 6s ºË ¾×: /

:  @A %ø.

 -]# lt+ /: ºË RF ¾‘ 6`w  ºË WB: sheath!"# sheath ¾B ƒ%:  ¾B&cw 8

¾c H¯ º5`k ?rvw Í`kx . t2w º Ë C^ RF ¾‘€5 aO ºË †%+ JUÈ¿ f¾É

˜kzvw÷ ?r Íc H: j<â N"D ˜kq  >

  ? Õu. ­˜ NOP ™ 'cZ ©/ ?r W B sheath %?< ‹v| plasma beam  ©Z^.

3.   

3-1.  (DC Self Bias Voltage)

Fig. 3 100 mTorr: Ҝ?ɑ# ºË 6s RF ¾‘: € 5 až ºË %ø JUÈ¿ f¾É dÏ( . RF ¾‘

 Lz aO JUÈ¿ f¾É Jvw Lc< ‹= þ)

 ÅØö Lc ªƒö Lc • ©6. § JUÈ

¿ f¾É ÕÚÖ K<s ™f ¾× RF ¾‘ 6s ºË ¾

×: /:  @A %ø vw ?r Íc H:  j<â flux ˜kq vw Z^.

3-2.  (Deposition Rate and Refractive Index)

Fig. 4 ºË 6s JUÈ¿ f¾É: €5 až LM º

 í8+ m dÏ( . JUÈ¿ f¾É Lz aO L M º Ç: Jvw ™*c °5`k < b™ ©6.

LMs :
, ™ : +, 5'bÜ g, tu= ,

×È -*. '/`k >. Fig. 5 ºË 6s JUÈ¿ f

¾É: €5 až
, ™(n) dÏ(. ºË 6s JU È¿ f¾É: L aO ¶? ÅØö Lc ªƒö ™*

+.
, ™(n) JUÈ¿ f¾É −50 V# −300 Vw L0  @ 1.89# 2.35w L+. A1 :c/ DLC: :
,

™ LMs : ]l aO €5+= ©=`k >. êÒ

vw ™evw  n2(1.9 !) =gÈ  dÏ3=, 

    :
, ™ 2 2.1-2.2 dÏ3

= © ï ” n2 LMs  4-5c • dÏ(= ©

=`= >[21]. t2w,  -]# LMs   ºË

6s JUÈ¿ f¾É(−50 V)# =gÈ  (polymer-like carbon) k<= 0*  JUÈ¿ f¾É(−300 V)# 4-5 s (graphite-like carbon) kŽ û  >.  Oƒ:

gÌ m# # dÏd >.

Fig. 2. Spatial distribution of average potential in RF-powered diode reactor.

Fig. 3. Effects of applied RF power on Grid DC self bias voltage at 100 mTorr.

Fig. 4. Effect of DC self bias voltage on deposition rate at 100 mTorr.

 39 1 2001 2

3-3.  (Optical Bandgap)

Fig. 6 3´: ž ºË 6s JUÈ¿ f¾É: €5 až

' j<  ¢c? B+ Tauc: plot dÏ(. êÒ

vw ¯ È-  !"# Ð ´: Ws !" d Ï(. cd α 10⁴cm⁻¹© ” Tauc !"= ž cd 

 j< BÞ+ !". hƒe# ¾ew ¾È 3 J n pc j< dÏ3 ¾?6  ½Í+ ' 

 Tau !"# ): 56 ™'6vwfF ¢`k^

[22].

Z?# α 7 =, E j<, β 8™, tu= Eg

'  dÏ(. ºË 6s JUÈ¿ f¾É −100 V,

−200 V,tu= −300 Vê @ Eg2 òò 2.35, 1.65, tu= 1.35 eVÊ

. A1 :c/ Eg ” π-m³ œ·¿ Q? " 8+= û çT >? @A[23] ºË 6s JUÈ¿ f¾É Lz

ë­ö C`k >< ‹vd j<  H :+ C-Hm³:

X sp²m³, sp³ ]lË tu= 0<= m³(dangling bond) : Ö >^ ~ vw Z^. ?³s π m³ [•@ )

=u¯ 5 5³&# j</# 78c? @A JUÈ

¿ f¾É Lz aO Lq vw ?es. Robertson[23]

 )6  ” œ·¿: Q?, N E_gâ: 8{6 '6

˜7cÊ.

Z?# E_go ¨< cd: )=u œ·¿â -'s j<= t

Ü2 6.0 eV. í8+ Eg2vwfF ¢+ N: 2 5.76,

13.2, tu= 19.75w JUÈ¿ f¾É Lz aO Ç: J

vw L+.

3-4. Raman !" #$ %& '(

Fig. 7 4´: ž JUÈ¿ f¾É# LMs DLC e+

1,100 cm⁻¹-1,700 cm⁻¹: !"# ˜1 Oƒ D¯ dÏ(.

A1 :c/ DLC 1,580 cm⁻¹þ: G(G “graphitic”:–) â 1,360 cm⁻¹þ: D(D “disorder” :–): Ð ´: Ws Oƒ A ý dÏ(= ©=`= >[24-26]. −50 V: JUÈ¿ f¾É

# LMs  Bö =gÈ   # '`k<

8+ Oƒ àQ dÏ3< ‹ [27]. § Oƒ ’(: fC Oƒ

’(: }< [Cc f2ÿ : &+ D–EFD ? @ A.  mwfF  JUÈ¿ f¾É# LMs  =G

: =gÈâ  sp³ C-Hm³ \ z½c= >  dÏ(

. −100 V™: JUÈ¿ f¾É# LMs : * efg:

DLC# '`k<  º 4- –ù m8¿(graphite crystallites)

 \ z½s  :–c H G y+ D <?. O

ƒ D >k# op+ €¯ G e+ D: ! /

6 &: (ID/I_G), G: àQ BÞ(ω_o), tu= GàQâ DàQ:

FWHM(Full Width at half-maximum)(Γ). ID/I_G  °z`k

> sp²: g7 dÏ3  „O sp²]l: ?¥ dÏ3 4 - –ù m8¿: Q? 8c= 4-5 8 8+= ûçT

>=[24, 25], : =½ É DSD '¾È  WX

w ý ~w G: BÞ BIvw ý ~ m ½†+

= ûçT >[28]. V+ GàQ: FWMH 4-: m8¿ Ö d αE

( )^{1 2⁄} =β(E E– _g)

E_g=E_go N --- Fig. 5. The variation of refractive index of DLC films deposited at dif-

ferent DC self bias voltage and 100 mTorr.

Fig. 6. Tauc’s plot depending on DC self bias voltage for calculating optical Bandgap at 100 mTorr.

Fig. 7. Raman spectra of DLC films prepared at different DC self bias voltage and 100 mTorr in the wavenumber from 1,100 cm⁻¹ to 1,700 cm⁻¹.

Ï(= ©=`= >[29, 30]. Fig. 7# −100 V# −300 VJ<:

JUÈ¿ f¾É# LMs : Oƒ D¯ * 7 K

àL :C deconvolution+ m Fig. 8 dÏ3M= ¢s Wp

€¯ Table 2 dÏd >.  mwfF JUÈ¿ f¾É

−100 V# −300 Vw Lz aO I_D/I_G 0.79# 4.48w L+

vw © = JUÈ¿ f¾É# LMs  4-5 >^`kŽ

©ZW=, GàQ: BÞ −100 V: 1542.9cm⁻¹# −300 V: 1588.6cm⁻¹ w BIvw ý = j<: hiw 6+ LM C^ : É

 DSD @A6 vw Z<|, GàQ: FWMH −100 V: 176.42 cm⁻¹# −300 V: 87.38 cm⁻¹w }s  –ù m8¿ 4-

= j<H hiw 6cZ œ· ^_`k m8¿ 4-vw `k

^ vw Z^.

4. 

?r Íc H j< 4 flux: ˜k Ÿ+ NOP Æ 8 :Ç+ RF ion source ˜Nc=,  cZ ?r JUÈ

¿ f¾É 6c< ‹=      LM cÊ.  CH4 H2D cZ ?r hic H j<

4 flux ˜kc? BC H ºË 6s JUÈ¿ f¾É € 5 ~/# _cÊv|, LMs : ]l 4  Ellipsometer, UV/VIS Spectroscopy, Raman 9 cZ
, ™, ' ,

-Š: m³ ]l 9 gÌcZ ): m M.

(1) H ºË 6+ JUÈ¿ f ¾É −50 V# −300 VJ

< L « aO
, ™ 1.89# 2.35w LcÊ=, (2) −100 V# −300 Vw L « aO '  2.35#

1.35w }cÊv|, ID/I_G:  0.79# 4.48w LcÊ.

§ mwfF,  RF ¾‘ 6w 6+ JUÈ¿ f¾É c / =gÈ     LM`k <= 0*  JUÈ¿

f¾É c/ LMs  4-5(graphite)+  LM9  û  >M. V+ Ý?Š <d : ŒŽ(peel-off)d O PÀPcZŽ(buckling) ¬ bx:    

   >M.

 

 QA 1998R +S 'T^UC¨: ’^-] <Õ˜ - ] :cZ _`Mv|,  }Í V„.



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Table 2. The main Raman parameters calculated from Gaussian curve fitting of Raman spectra for films deposited at DC self bias voltage of (a) −−−−100 V, (b) −−−−200 V, and (c) −−−−300 V, and 100 mTorr

Samples D Peak G Peak

I_D/I_G ω_o(cm⁻¹) Γ(cm⁻¹) ω_o(cm⁻¹) Γ(cm⁻¹) Grid

DC bias Voltage

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−300 V 1364.7 356.73 1588.6 187.38 4.48

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